The polyphenylene (oxide) ether resins are a well-known family of linear thermoplastic engineering resins. A wide variety of these resins and a number of methods for their preparation are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, as well as in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358.
It is known from Cizek, U.S. Pat. No. 3,383,435, among others, that polyphenylene ether resins can be compatibly admixed with polystyrene over a wide range of proportions.
Kambour in U.S. Pat. No. 3,639,508 and Haaf in U.S. Pat. NO. 4,167,507 teach that such composites can be modified for greater resistance to fracture upon impact by including elastomeric block copolymers of a vinyl aromatic such as styrene and a diene such as butadiene. These compositions are not entirely satisfactory, however, because of their relatively high melt viscosity which makes it difficult to extrude and mold them at temperatures considered advisable to avoid degradation or destabilization of the resins.
It has been observed with such compositions that a reduction in molecular weight of the homopolystyrene moiety causes a reduction in the notched Izod impact strength. The latter is an important property for engineering thermoplastic in general and polyphenylene ether resins and composition in particular and measures the ability of the molded part to resist fracture upon impact. At the same time, however, the molecular weight reduction effects a marked decrease in the melt viscosity of the composition, which is very desirable for ease of processing.
There remains a need for impact modified composites of a polyphenylene ether resin and polystyrene which exhibit a combination of low melt viscosity and high Izod impact strength.